1. Field of the Invention
This invention relates to humidity controllers for controlling humidifying and dehumidifying apparatus to maintain the humidity within a given environment at a set point value, and more particularly, to a humidity controller having a differential range adjust which remains constant with adjustment of the set point.
2. Description of the Prior Art
Humidity controllers are employed in environmental control systems for controlling apparatus of the system to maintain the humidity within a given area or environment at a set point value. A humidity sensor located within the area provides an output indicative of the % relative humidity within the area, and the output is used to effect energization of humidifying or dehumidifying apparatus for increasing or decreasing the humidity within the environment in accordance with deviations of the humidity from the set point value.
Generally, the humidity controller employs a differential detector including a pair of detector circuits. A first detector circuit controls the dehumidifying apparatus, and a second detector circuit controls thee humidifying apparatus. The detector circuits have different threshold settings to permit enabling of the first detector circuit whenever the humidity as sensed by the humidity sensor increases a pre-determined amount relative to the set point which is established by a set point means and to permit the second detector circuit to be enabled whenever the humidity decreases a pre-determined amount relative to the set point. The set point means is adjustable to permit selection of a desired set point for the humidity in the area. The humidity controller also includes means for establishing differential between the threshold levels for the first and second detector circuits. It is desirable that such differential also be adjustable over a given range. In known humidity controllers, once the differential range is established for a given set point, a change in the set point will cause a change in the differential range, and thus readjustment of the differential range is necessary whenever the set point is changed. This is undesirable because in normal operation, it is desirable to change the set point from time to time to provide the desired humidity for different atmospheric conditions, and without readjustment of the differential range, the response of the humidity controller will be different whenever the set point value is changed. Therefore, it would be desirable to have a humidity controller wherein the differential range once established for a given set point remains the same even when the set point is changed.